1. Field of the Invention
The invention relates to a communication system in a motor vehicle which is designed to participate in a chain-like ad-hoc radio network between motor vehicles and has a control unit and a transmission/reception unit connected to the control unit. The invention also relates to a method for setting up a wireless chain-like ad-hoc radio network between motor vehicles.
2. Description of the Related Art
Ad-hoc radio networks including a number of motor vehicles are also known by the term “car-to-car communication”. Within such a radio network, the motor vehicles can exchange information with one another. This can be, for example, information about hazard locations, the conditions of the roadway or also the approach of a motor vehicle having priority, or the like.
Each of the participating motor vehicles has a transmission/reception unit having a low transmitting power. The transmitting power is dimensioned, for example, in such a manner that only a connection to adjacent motor vehicles can be initiated. Overall, however, a radio chain between the individual motor vehicles involved is set up in this arrangement so that information can also be communicated to a motor vehicle from a motor vehicle further distant outside its own radio range. Such a communication system is disclosed in EP 1 223 567 A1.
If an inquiry is sent out from a motor vehicle to other motor vehicles via such an ad-hoc radio network, there is only an interest, as a rule, in responses from such motor vehicles which travel the road in the same direction of travel. Motor vehicles which travel in the opposite direction of travel encounter, for example, other traffic conditions, particularly in the case of roads having separate roadways for the two directions of travel. If the motor vehicles have a navigation system, the direction of travel can also be inferred by means of the data determined by the navigation system and this information can be transmitted together with the inquiry. Other motor vehicles which also have such a navigation system in which their own position is determined, for example by means of known methods such as satellite position finding and “map matching” including map data, can now determine whether they are underway in the same direction of travel of the road as the inquiring motor vehicle and decide correspondingly whether a response is transmitted or not. Although navigation systems are relatively widely used in the meantime, the greatest proportion of motor vehicles in existence does not yet have such a system and it cannot be expected in the future, either, that all motor vehicles will have navigation systems.